1. Field of the Invention
The present invention relates to a method of design for a partial circuit of a library cell, such as an AND circuit, a NAND circuit and an inverter circuit, of a reusable IP (intellectual property), such as an operational amplifier, an AD converter, a 32 bit multiplier and a CPU, and of the like, which are utilized in an integrated circuit such as an LSI.
2. Prior Art
It is general for a library design in an integrated circuit to be carried out by reusing circuit information and layout information of a library cell in the preceding process in order to shorten the number of design steps based on process technology information. As for a conventional method of design, there is a method for reducing the scale of the transistor size, or the like, used in the preceding process technology in a constant proportion by using a proportional constant in accordance with the change of the design rules, such as for the wire width. On the other hand, as for a method for optimizing the circuit performance, there is a method for optimizing the transistor size based on a design index, such as minimizing the delay, as disclosed in the Japanese patent 2872990.
In order to achieve the improvement of the performance or the reduction of the area of an integrated circuit, it is necessary for the individual library cells which form the integrated circuit to be optimized in performance and in area. A library cell, however, has different characteristics in accordance with the utilization conditions in the actual integrated circuit. Therefore, in designing a library cell it is necessary to carry out the optimization of the library cell under utilization conditions that are closer to those of the actual integrated circuit.
In a conventional method for design of a library cell, however, there is no method for precisely estimating, at the time of designing the library cell, under what conditions each of the library cells will be utilized in the actual integrated circuit. Therefore, the integrated circuit, which is formed of those library cells, has a problem such that sufficient operational speed cannot be gained or costs for extra area or power consumption are increased in order to secure the operational speed.
In addition, external conditions, such as the output load capacitance or the drive resistance of the input signal, at the time individual library cells included in the library are utilized in the integrated circuit, which is the design objective, are not unitarily determined for the technology but, rather, differ greatly due to the scale of the circuit, which is the design objective, or the types of circuit. Furthermore, even concerning the same circuit scale and type, since the same library cells are normally utilized in a variety of places in an integrated circuit, there is the problem that the external conditions cannot be precisely estimated at the time of designing the library cell.
In addition, at the time of design, trade offs of a variety of design indices, such as delay, area, power consumption and withstand against noise, exist and there is the problem that there is no method for the optimization of this plurality of indices from the viewpoint of trade offs.
In addition, in designing an IP which is a reusable macro block such as an operational amplifier, an AD converter, a 32 bit multiplier and a CPU, there is a case of design for utilization in other external conditions, such as ones where an IP which is a part of an already designed circuit (partial circuit) is utilized for a different technology, and a case of design with a presupposition, from the start, of the utilization under a plurality of external conditions. Accordingly, in the case of an IP, in the same manner as in the library cells, design is carried out under different external conditions or at a stage where the external conditions for this time are not seen and, therefore, there is the problem that the IP cannot be said to have optimal performance.
The purpose of the present invention is to provide a method for design of a partial circuit which can design a partial circuit, such as a library cell or an IP, so as to suitable for the external conditions at the time of the actual utilization on an integrated circuit.
A method for design of a partial circuit according to the present invention is a method for designing a partial circuit which designs a partial circuit of an integrated circuit characterized by including the step of external condition estimation, which estimates the external conditions of a partial circuit at the time of usage on an integrated circuit and the optimization step for designing the partial circuit according to the external conditions.
The step of external condition estimation is provided in this configuration and a partial circuit is designed according to the external conditions so that a partial circuit of which the performance is optimal for the external conditions can be designed.
In addition, in the present invention, the step of external condition estimation estimates the external conditions of a partial circuit based on technology information of an integrated circuit which is the design objective.
In addition, in the present invention, the step of external condition estimation includes the step of technology conversion which technologically converts the layout for external condition extraction which is prepared in advance based on technology information of an integrated circuit which is design objective, the step of layout extraction which extracts layout extraction information, that is external information which influences the operation of the partial circuit, from the layout for external condition extraction which has been technologically converted and the step of external condition calculation which calculates the external conditions of the partial circuit from the layout extraction information.
In this configuration, since the step of external condition estimation comprises the step of technology conversion, the step of layout extraction and the step of external condition calculation, it becomes possible to easily and precisely estimate the external conditions of a partial circuit in the technology, which is the design objective. In this case, the layout for external condition extraction, which has been prepared in advance, may include one, or more, partial circuits, which are the design objective, and may comprise arrangement information and wiring information of the partial circuits. In addition, the technology information of the integrated circuit, which is the design objective, may include one, or more, pieces of information from among information of the wire width, the minimum size of transistors and the wire gap.
In addition, the layout for external condition extraction which has been technologically converted in the step of technology conversion may be provided with the step of wiring which carries out rewiring based on the technology information of the integrated circuit, which is the design objective, so that in the step of layout extraction, the layout extraction information may be extracted from the layout for external condition extraction wherein rewiring is carried out in the step of wiring. In this case, since the step of wiring, which carries out rewiring, is provided, the value of the wire length, or the like, can be made closer to the value in the actual integrated circuit so that more precise external conditions can be easily estimated.
In addition, the layout for external condition extraction which has been technologically converted in the step of technology conversion may be provided with the step of compaction which carries out compaction so that in the step of layout extraction, the layout extraction information may be extracted from the layout for external condition extraction wherein compaction is carried out in the step of compaction. In this case, said the step of compaction is provided, the value of the wire length, or the like, can be made closer to the value in the actual integrated circuit so that more precise external conditions can be easily estimated.
In addition, the layout for external condition extraction which has been technologically converted in the step of technology conversion may be provided with the step of wiring which carries out rewiring based on the technology information of the integrated circuit, which is the design objective and, at the same time, may be provided with the step of compaction which carries out compaction for the layout for external condition extraction where rewiring has been carried out in the step of wiring so that in the step of layout extraction, layout extraction information may be extracted from the layout for external condition extraction wherein compaction has been in the step of compaction. In this case, since both the step of wiring, which carries out rewiring, and the step of compaction, the value of the wire length, or the like, can be made additionally closer to the value in the actual integrated circuit in comparison with the case where only one of them is provided so that more precise external conditions can be easily estimated.
In addition, in the present invention, the step of external condition estimation may estimate different external conditions in two, or more, partial circuits while the step of optimization may design each partial circuit under different external conditions in accordance with the partial circuit. In this case, since different external conditions are found for each partial circuit and each partial circuit is designed in accordance with the respective external conditions, the external conditions of a partial circuit can be more precisely estimated so that a partial circuit of high performance can be designed.
In addition, in the present invention, the step of external condition estimation may estimate external conditions in accordance with two, or more, integrated circuit, which become the design objectives, and the step of optimization may design a partial circuit in accordance with each integrated circuit. In this case, since external conditions of a partial circuit in each integrated circuit are estimated based on the technology information of the integrated circuit in the step of external condition estimation and each partial circuit is designed based on each external condition and on design indices of each integrated circuit in the step of optimization, it becomes possible to easily design a partial circuit which is optimal in accordance with respective integrated circuits.
In addition, in the present invention, the step of optimization uses a simulation circuit wherein a circuit expressing the external conditions estimated by the step of external condition estimation is connected to an external terminal of a partial circuit and designs the partial circuit based on the given design indices while evaluating the performance of the simulation circuit. In this manner, a partial circuit is designed based on the design indices and, therefore, it becomes possible to design a partial circuit which is optimal in accordance with the design indices.
In addition, two, or more, design indices may be given to the step of optimization so that a partial circuit may be designed in accordance with each design index based on each design index. In this case, since the partial circuit is designed based on two, or more, design indices, it becomes possible to design a partial circuit which is optimal in accordance with respective design indices.
In addition, in the present invention, the step of evaluation which evaluates the performance of a partial circuit, which has been designed in the step of optimization by using a circuit for evaluation, may be provided. In this case, an evaluation of the designed partial circuit can be easily carried out by, only, replacing the designed partial circuit with a partial circuit of the circuit for evaluation.
In addition, in the step of optimization, two, or more, design indices are given so as to provide the step of evaluation for evaluating the performance of the two, or more, designed partial circuits by using the circuit for evaluation at the time of designing the partial circuit in accordance with each design index based on the design index and the step of selection which selects a partial circuit based on the evaluation result of the step of evaluation. In this case, the designed partial circuit is replaced with a partial circuit of a circuit for evaluation so as to be evaluated and an optimal partial circuit can be easily selected.
In addition, in the present invention, partial circuits are circuits such as library cells or IPs.
In addition, in the present invention, partial circuits may be library cells and the external conditions may include at least one of the power source voltage of the library cells, the input signal waveform, the input drive resistance, the input current and the output load capacitance.
In addition, in the present invention, partial circuits may be circuits of two types, or more.